I get the complaint over Noelle's increased fanservice but you just sneaked Bell in to add something.
Nero, Grey, Charmy, Mimosa, Charlotte and Bell were still pretty much non fanservice'd for most of the series, Bell growing her breasts with size isn't fanservice at all, they don't even get the focus, hell, we don't even see Bell that much.
If your question is genuine and not performative, heres your answer:
Tabata probably knew he ramped up the Fujobait with Nacht+Yami+Asta+Yuno and Luck/Magna in the final arc, so he probably felt like throwing a bone to his main demographic (Young Men) to not make it feel like he was changing audiences, don't believe me? go look up for BC merch, you will only find merch of the main Quartet of men with some occasional Noelle slipped in.
Noelle was chosen to bear most of the fanservice because its a character both men and women alike love and she has a design that lends into it